1.Field of the Invention
The present invention relates to transmission of information between an interchangeable lens for a camera and an adapter therefor.
2. Related Background Art
There is already known a system for mutual information transmission by mechanical or electrical manner between the camera body and the interchangeable lens. In such system, for example, the information on F-number of the interchangeable lens is transmitted from lens to the camera body, and, to an interchangeable lens capable of driving the diaphragm or the focusing lens by an incorporated motor, the driving information therefor is transmitted from the camera body.
In such interchangeable lens system, in case an adapter such as intermediate ring or a rear-focus converter is mounted, a part of the information transmitted between the camera body and the lens has to be corrected according to the optical characteristics of such adapter. For such correction there have already been proposed various methods, which have respective advantages and disadvantages. Also, in the commonly assigned Japanese Patent. Laid-open Application No. 1-137241, a system free from the drawbacks of the conventional systems is proposed. In brief, this proposal is to at first effect communication between the interchangeable lens and the adapter to fetch the correction data of said adapter into the lens, then to effect direct communication between the camera body and the lens for various controls, and to effect necessary corrections on the transmitted data on the lens side.
Also the U.S. Pat. No. 4,912,494 discloses a system in which the interchangeable lens is provided with a signal processing unit, which identifies the mounting of an auxiliary phototaking means such as an adapter and effects communication with a signal processing unit in the camera body.
As explained in the foregoing, the data correction in the conventional technology is conducted in the interchangeable lens side. However, there are recently commercialized interchangeable lenses incorporating a motor for automatic focusing and provided with various additional functions, such as a go-home function for driving the lens to a pre-memorized position or a range limiting function for limiting the driving range of the lens. In such interchangeable lenses, the CPU thereof has considerable load for various controls, and the addition of corrective calculations for the adapters will create excessive loads, thus significantly deteriorating the functions of the entire system.